If we choose to live near convergent plate boundaries, we can build buildings that can resist earthquakes, and we can evacuate areas around volcanoes when they threaten to erupt. Yes, convergent boundaries are dangerous places to live, but with preparation and watchfulness, the danger can be lessened somewhat.
Nitrification, as stated above, is formally a two-step process; in the first step ammonia is oxidized to nitrite, and in the second step nitrite is oxidized to nitrate. Different microbes are responsible for each step in the marine environment.
Such effects have been shown in animal experiments, but their relevance to humans is uncertain because of the high doses and the specific amines used in these animals. In observational studies, intake of nitrate or nitrite from diet or drinking water is not associated with cancer in humans (3, 4). An effect of exogenous nitrite on cancer also seems less likely because large amounts of nitrite are formed endogenously. Fasting saliva contains â2 mg/L, and after consumption of an amount of nitrate equivalent to 200 g of spinach, the nitrite concentration in saliva may rise as high as 72 mg/L (7).